1. Field of the Invention
The present invention relates to an energy dispersive semiconductor X-ray detector (hereinafter called "EDS detector") which can be used, for example, in combination with an electron microscope to provide an energy dispersive type elemental analyzer such as an X-ray micro analyzer for measuring characteristic X-rays excited by electron beams and emitted from a sample, or a fluorescent X-ray analyzer that measures X-ray excitation.
2. Description of Related Art
EDS detectors have been used in energy dispersive type elemental analyzers requiring high resolution and they have incorporated a lithium drift type silicon semiconductor X-ray detector (Si(Li) detector). The advantages of this type of Si(Li) detector reside in its ability to provide high resolution, capability to simultaneously measure a large number of characteristic X-rays, and determine a spectrum of energy. A problem that has occurred, however, in a Si(Li) detector is that the lithium ions that are impregnated into the silicon to create an intrinsic detection region in the conventional detectors, however, may also continue inside the silicon as a result of thermal diffusion, thereby the characteristics of the detection can deteriorate and it is necessary to utilize a constant cooling system, for example, with liquid nitrogen, to combat this problem of thermal drift.
Reference can be had to FIG. 5 to show a conventional EDS detector wherein a cryostat 51 is provided so that it can ensure that the Si(Li) detection element 55 will be isolated from the external atmosphere. The cryostat 51 is connected to a Dewar 53 that contains liquid nitrogen 52 and a cold finger 54 having an L-letter shaped configuration is connected to and thermally linked to the Dewar 53, for example, by welding at one end, and at the other end, it supports not only the Si(Li) detection element 55, but also a FET 56 to provide a preamplification for an output signal. A window 57 is provided to permit X-rays 58 to penetrate through the window and enter the Si(Li) detection element 55. The inside of the cryostat can be maintained at a vacuum to help isolate the Si(Li) detection element 55 from atmospheric temperature problems.
The advantages of this conventional EDS detector shown in FIG. 5 is that it can prevent the thermal diffusion of lithium and decrease noise at the initial stages of the Si(Li) detection element 55 and the FET 56 as a result of the cooling by the liquefied nitrogen 52. A disadvantage is that it requires daily maintenance in order to replace the liquid nitrogen 52 that may evaporate.
Attempts have been made to replace the liquid nitrogen by using a small-size gas circulation system refrigerator such as a Joule-Thomson system or a pulse-tube type system. While such small-size gas circulation system refrigerators provide sufficient refrigeration capacity without a mechanical drive at its low temperature generation portion and thereby provides low vibration, easy maintenance and high reliability over a longtime period of operation, it still requires an AC power supply and any interruption of the power supply, such as a power failure or the need to transit the apparatus, can cause deterioration of the properties of the detection elements. To prevent this occurrence, it is frequently required that a standby power supply, such as batteries, be also installed, with a result of increase in size and cost.
Accordingly, there is still a desire within this industry to improve the performance of semiconductor X-ray detector systems.